Fruit trees can be vulnerable during Northwest winters. Some of the causes can be avoided, while others can only be watched out for and addressed should they arise.

Fertilizer: If your trees have new growth that has been killed or damaged by winter temperatures, it may be because the trees were fertilized after mid-August, which gives rise to tender growth that's unable to harden off before cold temperatures come.

Mulch: To encourage timely dormancy, wait until well into December to apply new mulches around fruit trees. If mulch is applied before fruit trees have gone dormant, it may prevent the ground from getting cold enough to help with dormancy, or slow the process. Temperature changes: During winter, after trees have gone into dormancy, temperatures may suddenly rise enough to cause sun scald, which occurs on the south or southwest side of the tree's trunk. When temperatures again drop, the cambium (the thin, greenish layer beneath the bark) is killed or damaged. The bark will usually crack open, though it's possible for the damage to remain hidden beneath intact bark. Sun-scalded areas usually lift away from the body of the tree.

Check all of your fruit trees after sudden or extreme temperature drops by tapping the trunk on the south and southwest sides. If there is a space beneath the bark, even if hidden, it usually sounds hollow when tapped. Tack down the bark along splits to reduce dehydration and help the tree recover.

The extent of the scald damage is usually more clearly defined in spring. Spring may also reveal damage you didn't detect earlier. If a tree has more significant freeze damage, resist pruning for that year. Bob Stebbins of Oregon State University says, "Freeze-injured trees that are not pruned often recover better than those that are -- they have larger leaf surface and can manufacture food and grow new conductive tissue faster than pruned trees."

After several of my fruit trees were severely scalded one winter, I began to apply white exterior latex paint to the first couple of feet of fruit tree trunks to help prevent more damage.

Wind: If a young fruit tree has been blown over by the wind while dormant, and half or less of the roots have been broken, chances are good that the tree can be saved. Dig for access to dislodged roots, and right the trunk until it is again vertical. Replace the roots to the appropriate depth; this is much easier with help. Prop and stake the tree so that it can re-anchor its roots. It may be necessary to prune the top back to reflect the loss of roots. This pruning makes the tree less vulnerable to wind, so the roots can re-anchor more easily. It also reduces the water needed by the tree. Be careful to irrigate well as the tree recovers. It may take four or five seasons to fully heal.

Broken branches should be pruned off, leaving the collar (the slight swelling at the base of the branch where it is attached to a larger branch or the trunk) intact so that the pruning wound can heal as quickly as possible. Take care not to leave a stub, which fosters the development of fungi that can rot the tree's wood.